Re: Urgent - Time to kill, want to build IR Extender

["Graham Howe" <graham@xxxxxxx>]

> >few questions (all of you electronics experts can feel free to
laugh at
my
> >stupidity!).
>
> I won't be laughing, at least not until I correct the schematic with
that
> stupid error of missing out the +12V connection :-)
>
I think I managed to put it in the right place

> >First off, the 555 timer has an indentation on the top, does this
indicate
> >pin 8, also are pin numbers ordered as per Nigel's diagram, if not
what
is
> >the sequence.
>
> ICs usually look like
>
> 8  7  6  5
>
> i  i  i  i
>
> o
> i  i  i  i
>
> 1  2  3  4
>

Yeah this is what I found from the RS site
>
> >Second, the LED's, I know that the shortest leg is the cathode,
does that
> >mean the other leg is the one to connect to the +12V.
>
> Probably.  Some LEDs are the other way round, there's no particularly
> common standard, if you can see inside, it looks a bit like a wire
going
> into a 'cup'.  The 'cup' is usually the cathode (I think, I usually
just
> test them with a battery!).
>
I was worried about blowing it if I did this and got it wrong, but I will
now try tonight

>
> >Third, the transistors, how do I know which leg is which. I have
assumed
the
> >diagram shows the plan view of the transistor, but there is a
little tag
by
> >one leg which I have assumed is number three on the diagram, is
this
correct
> >?
>
> Usually, though again not definitely, emitter (1 on the diagram) is
nearest
> to the tag.  If you have a multimeter with a diode test setting, it's
> possible to check the other pins, let me know if you want to know how.
The
> diagram is just a standard schematic layout, it might not correspond
to
the
> physical layout of the transistor you have.
>
> The Maplin catalogue usually has package pinouts for transistors,
check
> whether it is shown as 'view from above' or 'view from below'.  Where
the
> transistor is listed in the catalogue, it will say package type,
something
> like 'TO92', at the start of the transistors section there is usually
a
> page showing all the different packages and pins.
>
> Pin 3 on my diagram is collector (C), 2 is base (B), 1 is emitter (E).
 If
> that doesn't make sense, send me an email with the details of the
> transistor you have and I'll try to give more specific directions.
>
I'll have another look at the Maplins site tomorrow

> >Finally, is there any way I can test the transmitter without a
receiver
and
> >when I get a receiver (hopefully from Keith), where does that
connect to
the
> >transmitter ?
>
> There are 2 lines sticking out to the left of the diagram, with some
stuff
> about 'input' on them.  The lower one connects to the receiver's 0V
> connection, the other to the receivers output connection.  The
receiver's
> 3rd pin needs to be connected to +5V +/- 0.25V.
>
> The only way to test before the receiver arrives is using an
oscilloscope,
> a multimeter with a frequency meter, or a camcorder/camera.  If you
have
> any of those, let me know and I'll tell you what you can use it for.
>
I do have a camcorder (Hi8) and a digital camera, please do send
instructions for testing with these.

> >I am sorry for these really basic questions, but this is my first
ever
> >circuit and I would rather it didn't go bang as soon as I connect
the
power.
>
> Where's the fun in that   :-)  ?  I'm happy to try to help you get it
> sorted, feel free to email me directly if there are any more
questions-
> unless others on the list want to see more gory details?
>
I'll keep posting gory details here. Incidentally, I will be making the
other circuit too, though I am missing a component at the moment (the
photodiode). When both are working I'll do some basic comparison tests. One
other question, I am planning to link the receiver(s) to the transmitter
with CAT5 going through normal IDC connections. Should I avoid using both
wires in a twisted pair or is this OK ?

> Nigel
>
Thanks for all the help

Graham


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